'''
异常处理
'''
def demo1():
    numa = 100;
    numb = 200
    result = numa +numb
    return int(input("请输入一个整数："))

def demo2():
    return demo1()



def f1():
    print("F1")
    f2()

def f2():
    print("F2")
    f3()

def f3():
    print("F3")


if __name__ == '__main__':
    # try:
    #     print(demo2())
    # except ValueError:
    #     print("请输入正确的整数")
    # except Exception as result:
    #     print("未知错误 %s" % result)

    f1()